The sight of human beings, most of them unarmed, being gunned down from above is jarring enough.

But for many people who watched the video of a 2007 assault by an Army Apache helicopter in Baghdad, released Monday by WikiLeaks.org, the most disturbing detail was the cockpit chatter. The soldiers joked, chuckled and jeered as they shot people in the street, including a Reuters photographer and a driver, believing them to be insurgents.

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In recent days, many veterans have made the point that fighters cannot do their jobs without creating psychological distance from the enemy. One reason that the soldiers seemed as if they were playing a video game is that, in a morbid but necessary sense, they were.

“You don’t want combat soldiers to be foolish or to jump the gun, but their job is to destroy the enemy, and one way they’re able to do that is to see it as a game, so that the people don’t seem real,” said Bret A. Moore, a former Army psychologist and co-author of the forthcoming book “Wheels Down: Adjusting to Life After Deployment.”

Combat training “is the only technique that will reliably influence the primitive, midbrain processing of a frightened human being” to take another life, the colonel writes. “Conditioning in flight simulators enables pilots to respond reflexively to emergency situations even when frightened.”

The men in the Apache helicopter in the video flew into an area that was being contested, during a broader conflict in which a number of helicopters had been shot down.

Several other factors are on display during the 38-minute video, said psychologists in and out of the military. . . .

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The fighters in the helicopter say over the radio that they are sure they see a “weapon,” even though the Reuters photographer, Namir Noor-Eldeen, is carrying a camera.

“It’s tragic that this all begins with the apparent mistaking of a camera” for a weapon, said David A. Dunning, a psychologist at Cornell University. “But it’s perfectly understandable with what we know now about context and vision. Take the same image and put it in a bathroom, and you swear it’s a hair dryer; put it in a workshop, and you swear it’s a power drill.”

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After the helicopter guns down a group of men, the video shows a van stopping to pick up one of the wounded. The soldiers in the helicopter suspect it to be hostile and, after getting clearance from base, fire again. Two children in the van are wounded, and one of the soldiers remarks, “Well, it’s their fault for bringing their kids into a battle.”

Here again, psychologists say, when people are intensely focused on observing some specific feature of the landscape, they may not even see what is obvious to another observer. The classic demonstration of this is a video in which people toss around a basketball; viewers told to count the number of passes rarely see a person in a gorilla suit who strolls into the picture, stops and faces the camera, and strolls out.

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The soldiers were looking for combatants; experts say it is not clear they would have seen children, even if they should have.

The video’s emotional impact on viewers is also partly rooted in the combination of intimacy and distance it gives them, some experts said. The viewer sees a wider tragedy unfolding, in hindsight, from the safety of a desk; the soldiers are reacting in real time, on high alert, exposed.

In recent studies, researchers have shown that such distance tempts people to script how they would act in the same place, and overestimate the force of their own professed moral principles.

“We don’t express our better angels as much as we’d like to think, especially when strong emotions are involved,” Dr. Dunning said. He added, “What another person does in that situation should stand as forewarning for what we would do ourselves.”